JP3259869B2 - Electrode substrate for electrolysis and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a durable electrode substrate for electrolysis and a method for producing the same, and more particularly, to an electrolytic electrode substrate used at a high current density and having mainly durability against oxygen generation reaction and resistance against current reversal. The present invention relates to an electrode substrate for use and a method for manufacturing the same.

[0002]

2. Description of the Related Art Industrial electrolysis, particularly electrolysis mainly using inorganic acids, is performed in a very wide range such as electrolytic smelting of metals, electroplating, and electrolytic synthesis of organic and inorganic substances. These electrodes for electrolysis, particularly lead or lead alloy electrodes, platinum-plated titanium electrodes, carbon electrodes, etc., have been proposed as anodes, but all of these electrodes have drawbacks and are not used for electrolysis in a wide range of applications. For example, a lead electrode is formed on its surface with lead dioxide, which is relatively stable and has good conductivity. However, this lead dioxide also has the drawback that several mg / AH is dissolved under ordinary electrolysis conditions, and the overvoltage is large. Platinum-plated titanium electrodes are expensive and have a short life, and if the anodic reaction is an oxygen generating reaction, the carbon electrode reacts with the generated oxygen to consume itself as carbon dioxide and has poor conductivity. There is. Dimensionally stable electrodes (DSE) have been proposed and widely used to overcome the disadvantages of each of these electrodes.

[0003] As long as this DSE is used as an anode with a valve metal represented by titanium as a base, the surface is passivated and functions as a chemically extremely stable long-life electrode.
However, when the DSE is also used as a cathode and is subjected to negative polarization, it reacts with the generated hydrogen to become hydride, which weakens the substrate itself or peels off the surface coating due to corrosion, thereby significantly shortening the electrode life. In particular, this is a major drawback when using DSE for electrolysis where the polarity is reversed, that is, the current direction is reversed.

To avoid this, if nickel or stainless steel resistant to negative polarization is used, these materials cannot be used as an anode in a neutral to acidic solution, so that the polarity is reversed. It is clear that it is not suitable as an electrode for use. Also, carbon electrodes such as graphite, which are said to be resistant to both positive and negative polarization, tend to have their surface collapse with the generation of gas, especially when performing positive / negative reversal,
Even if it could be used theoretically, it was of little practical value.

Further, these intermediate layers and modified layers have resistance to the above-mentioned organic substances and certain corrosive halides, but they are not sufficient. There was a problem in that it relied on its own corrosion resistance. In order to prevent the above-mentioned disadvantages of the prior art, in particular, passivation of the intermediate layer, there has been proposed a method of forming an intermediate layer by spraying a tantalum wire (Japanese Patent Laid-Open No. 5-156480).
issue). It is reported that this tantalum spraying forms an intermediate layer composed of a partial oxide in which metal tantalum and tantalum oxide are mixed. However, tantalum is liable to be oxidized, that is, passivation is more likely to occur than other metals, and it cannot be expected to have a long life especially under severe conditions. are doing.

As described above, there is substantially no material stable in both positive and negative polarizations among the valve metals, iron group metals and alloys thereof. However, some ceramics, which are a kind of metal oxide, are stable to both positive and negative polarizations and provide a certain degree of conductivity. However, this conductivity is considerably smaller than that of metal, and since this kind of electrode used for industrial use must be a polycrystalline sintered body, it has a higher resistance. It was inappropriate.

[0007]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems relating to conventional electrode substrates, particularly substrates such as DSE, and has sufficient durability and chemical stability under a high current density, and has a positive / negative inversion. It is an object of the present invention to provide an electrode substrate for electrolysis which is stable for use under negative polarization in electrolysis or the like accompanied by an electrolytic solution and use in an electrolytic solution containing a corrosive substance and can be used for a long period of time, and a method for producing the same.

[0008]

SUMMARY OF THE INVENTION The present invention comprises a conductive metal substrate, and a platinum group metal, at least one metal selected from the group consisting of titanium, tantalum and niobium, and oxygen formed on the surface of the substrate. Non-stoichiometric partial oxide thickness 10 to 20
An electrode substrate for electrolysis comprising a coating layer of 0 μm.

Hereinafter, the present invention will be described in detail. A feature of the present invention is to form a coating layer made of a partial oxide having a non-stoichiometric composition containing a platinum group metal on a conductive metal base material, and to improve the conductivity and corrosion resistance inherent in the oxide. Utilizing, utilizing the resistance to the positive and negative reversal electrolysis and relatively large conductivity of the platinum group metal, has sufficient durability and chemical stability under high current density that could not be achieved by the prior art. Another object of the present invention is to provide an electrode substrate for electrolysis that is stable for use under negative polarization in electrolysis with positive / negative reversal and the like and for use in an electrolytic solution containing a corrosive substance and can be used for a long period of time.

The conductive metal substrate used in the present invention is not particularly limited as long as it is conductive because it is isolated by a coating layer formed on the surface when used as an electrode. For example, when used as an anode in a strong acid, it is desirable to use a valve metal represented by titanium or the like having relatively high corrosion resistance. The use of a titanium alloy is preferred. Of course, in other electrolysis, an iron group metal such as nickel or a corrosion-resistant alloy such as stainless steel or trade name Hastelloy can be used according to the purpose.

In the present invention, it is desirable to roughen the surface of the substrate before forming the coating layer on the substrate. Since the coating layer has a thickness of 10 to 200 μm as a surface layer, it has an anchor effect for holding the coating layer and obtaining stronger adhesion and a strong chemical bond between the substrate and the coating layer. The surface is roughened in order to obtain. Typical surface roughening methods include a physical method and a chemical method. This roughening is performed with care so that no impurities remain on the surface of the substrate after the roughening and a chemically unstable processed layer does not remain. Although the degree of surface roughening is not particularly limited, JISR _a = 10 to 20
μm, JISR _max = about 50 to 200 μm is desirable.

As a physical method of the above-mentioned roughening, for example, there is a roughening by blasting, and the surface of the base material is polished with a ceramic sand such as alumina to form irregularities. In the case of this blasting method, it is preferable to use alumina or silica which is resistant to acid or alkali as the blast powder in consideration of the possibility that the electrolytic solution penetrates to the substrate surface of the electrode finally formed. If alumina or the like is used, even if the powder remains on the surface of the base material, the electrode can be used stably without causing abnormal elution as an electrode. Of course, it is more desirable to carry out pickling treatment or the like in order to prevent the residue of these powders that have penetrated the surface.

The above-mentioned chemical surface roughening method is a method of forming irregularities on the surface of a substrate with a chemical to roughen the surface. For example, when using titanium or a titanium alloy as a base material, about 85 to 90 ° C.
By immersing the previously washed substrate in a 20% hydrochloric acid aqueous solution and holding it for several hours, intergranular corrosion occurs to roughen the surface. If the substrate is titanium or stainless steel, 40-60
By immersing the base material in an aqueous solution of iodic acid of about 10% of about 10 ° C., so-called pitting corrosion is caused to roughen the surface.

A coating layer containing a platinum group metal and a partial oxide may be formed directly on the surface of the base material. In particular, when the constituent metals of the base material and the coating layer are different, the base material and the coating There is a risk that the adhesion of the layer may be poor, and when thermal spraying is used, the risk is further increased. In this case, it is desirable to form a bonding layer made of a metal oxide between them. For the reason for the formation, the bonding layer is preferably a mixture of oxides of both the base metal and the coating layer forming metal. The bonding layer must be conductive, and is preferably a semiconductive oxide obtained by applying a solution of the constituent metal salt on the substrate and thermally decomposing the solution at 300 to 600 ° C. Alternatively, a semiconductive oxide can be formed in advance by forming a non-conductive oxide and then exposing the surface to a plasma flame to partially extract oxygen from the oxide.

Next, a coating layer containing a platinum group metal such as platinum, rhodium, ruthenium or iridium and a metal oxide having the same properties as the above-mentioned ceramics is formed on the surface of the roughened substrate or the surface of the bonding layer. To form The metal oxide comprises at least one metal of titanium, tantalum and niobium and non-stoichiometric partial oxides including these oxides. It is necessary that the coating layer has conductivity and substantially completely covers the conductive substrate or the bonding layer thereof. The partial oxide in the coating layer has a non-stoichiometric composition, that is, a composition formula RO _2-x (R represents a metal component and 0 <x <1
Is not particularly limited.

At least one oxide of titanium, tantalum and niobium in the coating layer is a ceramic itself and is stable against electrolysis containing a fluorine component and an organic substance mixed in the electrolytic solution. However, in the electrolysis where the polarity is reversed, it is much more stable than the metal substrate, but especially in the case of negative polarization, penetration of extremely small hydrogen ions cannot be completely prevented.
Hydrogen ions can reach the base metal through both the liquid and the solid, and the base metal can be destroyed during negative polarization.
In order to avoid this, in the present invention, by adding a platinum group metal to the coating layer, it is possible to provide an electrode that can withstand a true current reversal.

Although the true reason is unknown, it is thought to prevent the transfer of oxygen ions which occur when the substrate is used as an anode and the transfer of hydrogen ions which also occur when the substrate is used as a cathode. Can be The platinum group metal does not need to be present in a large amount, and it is sufficient that the amount is 5 g / m ² or less, but it is preferable that the platinum group metal is uniformly dispersed over the entire surface.

The coating layer containing the platinum group metal and the partial oxide may be formed by any method, but is preferably formed by a spraying method such as plasma spraying or arc spraying.
When a coating layer containing a metal and a metal oxide is formed on a metal substrate by thermal spraying, the coating layer becomes a unique and large-area surface layer unique to arc spraying or plasma spraying, and has a substantial current density when used in electrolysis. In addition, good conductivity by metal and strong adhesion between the thermal spray coating layer and the base metal can be secured, and conductive oxidation due to lack of oxygen in partial oxides caused by a large amount of metal. An electrode substrate for electrolysis having good resistance resulting from the formation of a product is obtained, and furthermore, the progress of passivation is suppressed due to oxidation resistance under ordinary electrolysis conditions of titanium or the like, and long-term use becomes possible.

The particle size of the spray particles to be used may be selected according to the purpose. Of course, it is desirable that the surface area is large as long as the electrode substrate is used. It is desirable that the surface roughness of the electrode substrate is approximately JISR _max ≧ 100 μm and JISR _a ≧ 10 μm. To achieve this surface roughness, spray particles having a particle size of 20 to 100 μm should be used. However, it is also possible to spray a wire. If the particle size is less than 20 μm, a dense coating layer can be formed, but the surface roughness becomes small and oxidation during thermal spraying may proceed too much. on the other hand
If it exceeds 100 μm, it is difficult to form a dense thermal sprayed layer without through holes. When only the metal is used as the thermal spray material, the thermal spray layer can be formed by using a metal wire as a raw material by the arc thermal spraying method. In this case, the density is inferior to the plasma spraying by about 5 to 10%, but there is a feature that the unevenness of the surface is correspondingly large, so that it can be selected according to the application. As the titanium oxide, tantalum oxide and niobium oxide used for thermal spraying, purified rutile ore, tantalite ore, and columbite ore can be used as they are.

The thickness of the coating layer to be formed is suitably from 10 to 200 μm, and if it is less than 10 μm, there is a great possibility that a through hole will remain. And the conductivity of the coating layer is 10 ^-2 to 10 ^-3 Ω.
cm, the ohmic loss becomes large under a high current density, and the local heat generation tends to shorten the electrode life.

In order to contain a platinum group metal in the coating layer by the thermal spraying method, a thin layer of a platinum group metal compound may be previously supported on the surface of thermal spray particles such as titanium metal and titanium oxide. That is, the surface of the metal and / or oxide particles to be sprayed is activated with a volatile acid such as hydrochloric acid and then immersed in an aqueous solution of a salt of a platinum group metal such as chloroplatinic acid or an alcohol solution, or the like, to thereby form the particle surface. Support a platinum group metal salt. The particles are dried and then heat-treated at about 400 to 800 ° C. to thermally decompose the compound to precipitate a platinum group metal on the surface of the particles, and then spray the particles on the surface of the base material, A coating layer made of a partial oxide in which a platinum group metal is dispersed can be formed. Since the platinum group metal compound on the particle surface before thermal spraying is heated by thermal spraying, it is not necessary to thermally decompose and reduce it to platinum group metal before thermal spraying, but it is necessary to perform thermal decomposition in advance to deposit platinum group metal. The yield increases the yield of platinum group metals.

It is not necessary to support the platinum group metal on all of the thermal spraying particles. The coating layer may be formed by spraying mixed particles of particles supporting the platinum group metal or its compound and particles not supporting the platinum group metal. . Further, a coating layer containing no platinum group metal is formed by thermal spraying or the like, and thereafter the platinum group metal and the partial oxide are deposited on the surface of the coating layer by vapor deposition or thermal decomposition so as to be uniformly dispersed. May be formed.

In order to form the above-mentioned non-stoichiometric partial oxide, the thermal spraying method is optimal. When a sprayed material is formed by ordinary plasma spraying, the sprayed material itself is in a strong reducing atmosphere, and no oxide is generated in this atmosphere. A surface may be formed. Conventionally, in order to prevent this oxide formation, an inert gas such as nitrogen or argon is used as a seal gas to suppress oxidation. However, in the present invention, which is intended to form a non-stoichiometric partial oxide,
Rather, utilizing the phenomenon of actively forming this oxide, only spraying metal particles converts a part of the sprayed metal to metal oxide and promotes non-stoichiometric composition to include conductive oxide It is intended to form a coating layer. As other methods for forming non-stoichiometric partial oxides by the thermal spraying method, there are the following two types of methods, namely, the use of an oxidizing seal gas and the method of forming an oxide by using oxide spray particles.

The sprayed metal particles and wire are sprayed onto the roughened substrate surface using a mixed gas of argon and helium according to ordinary spraying conditions. At this time, if the surrounding seal gas is an oxidizing gas, a part of the sprayed metal is oxidized to form a mixed coating layer which is a partial oxide containing the sprayed metal and the metal oxide. The amount of generated oxide varies depending on the conditions. For example, if the oxidizing gas is air and the particle size of titanium as a spray metal is 30 to 60 μm, 20 to 30% of the sprayed titanium is converted to titanium oxide, and 70 to 80%. A mixed coating layer is formed which is a partial oxide containing 2% by weight of sprayed titanium and 30% to 20% of titanium oxide. When the oxygen content is increased to about 50%, the oxide amount also increases to about 50%. However, if the amount of metal oxide is further increased, an insulating oxide may be formed and conductivity may be impaired, and oxidation may explosively proceed.

Further, not only the above-mentioned metal particles or wire but also a metal oxide powder or wire as a sprayed material is mixed and sprayed under the same spraying conditions to obtain a partial oxide containing metal and metal oxide at a predetermined ratio. Certain mixed coating layers are formed. It is sometimes desirable to include all metals and metal oxides of titanium, tantalum and niobium in the coating layer. In this case, the method of using the oxide powder as a part of the particle powder is very convenient because the ratio of each metal and the ratio of the sprayed metal and the sprayed oxide can be set to a predetermined value, and the present invention is applicable to a wide range of applications. It becomes possible to apply.

The electrode substrate of the present invention having the above-mentioned structure is coated with an electrode material containing, for example, iridium oxide to form an electrode. Have a much greater resistance than conventional electrode substrates, especially the ability to block the penetration of oxygen and hydrogen ions, thereby slowing passivation and thereby substantially extending the life of the electrode.

[0027]

EXAMPLES Next, examples of the production of an electrode substrate according to the present invention will be described, but the examples do not limit the present invention.

[0028]

Example 1 Purified natural rutile ore and tantalite ore were mixed at a weight ratio of titanium and tantalum of 9: 1 and pulverized by a ball mill. Classify after grinding for 12 hours,
Those having a particle size of 20 to 50 μm were selected. This mixed particles
After dispersing in 20% boiling hydrochloric acid and keeping the mixture for 30 minutes, it was washed with city water to remove iron. By this operation, some particles become 20
Since the particle size was less than μm, the particles were removed by wet classification.

The remaining particles were dried, and 30% of the particles were immersed in chloroplatinic acid, then taken out and cut off in an oven.
The particles were baked at 550 ° C. for 1 hour to carry metallic platinum on the surface of the particles. The platinum loading was 2 g / 100 g-particles. 30% of particles supporting platinum were sufficiently mixed with 70% of particles not supporting platinum to obtain a powder for plasma spraying.

On the other hand, length 100 mm, width 100 mm, thickness 3 mm
Using a commercially available JIS type 2 pure titanium plate as a base material, the surface was sandblasted with alumina sand having a diameter of 1.2 mm to break the surface structure, and the surface was washed and degreased with acetone. An argon gas containing 10% of helium was used as a plasma gas, and the powder for plasma spraying was sprayed on the surface of the titanium as a base material to form a coating layer having a thickness of about 100 μm. The amount of supported platinum is calculated as 3
g / m ² . The surface roughness of the formed sample substrate is R
_max = 200 μm.

An electrode material, which is a 2: 1 (molar ratio) mixture of iridium oxide and tantalum oxide, was formed on the surface of the sample substrate by thermal decomposition to form a sample electrode. The coating amounts were 7 g iridium / m ² and 3 g tantalum / m ^{2, respectively.}
Met. The two sample electrodes were immersed in an aqueous solution of sulfuric acid containing 250 g / liter of sodium sulfate adjusted to a pH of 0.5 to 1, and maintained at a temperature of 60 ° C., and the current was applied while inverting the polarity every two minutes to perform electrolysis. went. The current density was 300 A / dm ² , and electrolysis could be continued even after 1200 hours.

[0032]

Comparative Example 1 A sample electrode was prepared in the same manner as in Example 1, except that platinum was not supported on all particles.
When electrolysis was performed under the same electrolysis conditions as in Example 1 using this sample electrode, electricity could not be supplied 700 hours after the start of electrolysis.

[0033]

EXAMPLE 2 A powder of titanium: niobium: tantalum = 16: 3: 1 (molar ratio) before carrying platinum was prepared in the same manner as in Example 1, except that columbite was used instead of tantalite. . This powder was pickled and iron-removed in the same manner as in Example 1, and titanium sponge whose particle size was adjusted to 10% with respect to the amount of titanium was added and mixed well. The particles were immersed in a solution of chloroplatinic acid in isopropyl alcohol, and then dried in air at 100 ° C. to obtain a thermal spray powder. Platinum loading is 5g
/ Kg-particles.

On the other hand, the same pure titanium plate as in Example 1 was used.
After sandblasting in the same manner as described above, the surface was activated by treatment in 20% boiling hydrochloric acid to obtain a substrate. A 5% hydrochloric acid aqueous solution of titanium tetrachloride and tantalum pentachloride was applied to the surface of the base material so that titanium: tantalum = 9: 1 (molar ratio), and baked at 540 ° C. for 15 minutes in flowing air. This was repeated twice to form a binding layer made of a rutile oxide.

The thermal spraying powder was plasma-sprayed on the surface of the bonding layer under the same conditions as in Example 1 to form a coating layer having a thickness of about 100 μm. The amount of platinum carried was about 3 g / m ² in terms of yield calculation, and the surface roughness of the formed sample substrate was R _max = about 220 μm. After the same electrode material as in Example 1 was coated on this sample substrate by the same operation as in Example 1, electrolysis was performed under the same electrolysis conditions as in Example 1. The electrolysis was continued even after 1200 hours from the start. Was possible.

[0036]

Example 3 A thermal spraying powder in which all particles did not carry platinum was prepared according to the procedure of Example 1, and the thermal spraying powder was plasma-sprayed on the same substrate as in Example 1 to contain platinum. No covering layer was formed. Platinum was deposited on the surface of the coating layer by a physical vapor deposition method so that the amount of platinum carried was 3 g / m ^2, and was held at 600 ° C. for 3 hours to be sufficiently diffused. The surface was coated with an electrode material in the same manner as in Example 1 to obtain a sample electrode. Positive / negative inversion electrolysis was performed using the sample electrode under the same conditions as in Example 1. As a result, an electrode life of 1300 hours was obtained.

[0037]

According to the present invention, there is provided a conductive metal substrate, and a non-stoichiometric composition comprising a platinum group metal, at least one metal selected from the group consisting of titanium, tantalum and niobium, and oxygen formed on the surface of the substrate. An electrode substrate for electrolysis, comprising a coating layer of a partial oxide having a thickness of 10 to 200 μm.

Although the electrode substrate according to the present invention has resistance to a high current and resistance to fluorine components and the like even with only the partial oxide in the coating layer, the resistance at the time of positive / negative inversion electrolysis is not sufficient. However, the platinum group metal present together with the partial oxide has resistance to the positive / negative inversion electrolysis, and the coating layer has resistance to high current and fluorine components, as well as resistance at the time of positive / negative inversion electrolysis,
The coating layer protects the electrode substrate almost completely, and the effective electrode life is extremely long.

When the adhesion between the metal substrate and the coating layer is likely to be insufficient, the metal oxide containing the metal constituting the substrate and the coating layer preferably between the two, that is, on the surface of the substrate. The adhesion can be improved by forming a bonding layer made of a material.

In order to form the coating layer containing the platinum group metal and the partial oxide on the base material to produce the electrode substrate for electrolysis according to the present invention, a layer containing only the partial oxide is required. Is formed on the base material, and then a platinum group metal is added to the layer by vapor deposition or thermal decomposition to form a coating layer, or a metal or metal carrying a platinum group metal as in the case of thermal spraying. An oxide can be prepared in advance and coated on the substrate to form a coating layer.

Continuation of front page (56) References JP-A-7-54182 (JP, A) JP-A-6-33287 (JP, A) JP-A-5-148675 (JP, A) JP-A-4-301062 (JP) , A) JP-A-7-62584 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C25B 1/00-15/08

Claims (5)

(57) [Claims] 1. A conductive metal substrate, and a partial oxidation of a non-stoichiometric composition formed on the surface of the substrate and containing a platinum group metal, at least one metal selected from titanium, tantalum and niobium, and oxygen. An electrode substrate for electrolysis, comprising a coating layer having a thickness of 10 to 200 μm. 2. A conductive metal substrate, a bonding layer formed of a metal oxide formed on the surface of the substrate, and at least one of a platinum group metal, titanium, tantalum and niobium formed on the surface of the bonding layer. An electrode substrate for electrolysis, comprising a coating layer of a non-stoichiometric partial oxide containing a kind of metal and oxygen having a thickness of 10 to 200 μm. 3. A coating layer having a thickness of 10 to 200 μm of a non-stoichiometric partial oxide containing at least one metal of titanium, tantalum and niobium and oxygen on a conductive metal substrate. An electrode substrate for electrolysis, wherein a coating solution containing a platinum group metal compound is applied to the surface of the coating layer, and the platinum group metal compound is thermally decomposed to disperse the platinum group metal in the coating layer. Manufacturing method. 4. A coating layer having a thickness of 10 to 200 μm of a non-stoichiometric partial oxide containing oxygen and at least one metal of titanium, tantalum and niobium is formed on a conductive metal substrate. Then, a platinum group metal is deposited on the surface of the coating layer,
A method for producing an electrode substrate for electrolysis, comprising dispersing the platinum group metal in the coating layer. 5. Spraying particles of at least one kind of metal and / or metal oxide of titanium, tantalum and niobium having at least a part of which supports a platinum group metal or a compound thereof on a conductive metal substrate. Forming a coating layer having a thickness of 10 to 200 μm of a partial oxide having a non-stoichiometric composition containing a platinum group metal, at least one metal of titanium, tantalum and niobium and oxygen. For producing an electrode substrate for use.